1. Field of the Invention
This invention relates to the field of micro-electromechanical systems (MEMS). In particular, the invention relates to a system and method for canceling ringing in tunable members of MEMS devices.
2. Description of the Related Art
The field of Micro-electromechanical systems (MEMS) are devices containing miniature mechanical parts, often contained within a silicon substrate. These tiny mechanical may include members such as gears, mirrors, sensors, or valves embedded in semiconductor chips. Such devices may be fabricated in large quantities, exploiting techniques developed for the manufacture of silicon wafers. Domains in which the technology may be applied include opto-electronics, microfluidics, and control systems.
A substrate including a MEMS device may also incorporate electronic circuitry which may be used to control the MEMS device. Although the prior art includes similar control systems applied to other mechanical technologies, these techniques have proven inadequate of MEMS technology. As such, there is a need for including control circuitry in a MEMS device for canceling ringing in adjustable mechanical members contained in the MEMS device.
The invention includes a Finite Impulse Response (FIR) filter for suppressing ringing in tunable, or adjustable, members of MEMS devices. In embodiments of the invention, the FIR filter includes staggered proportional plus delay filters, or posicast filters. The FIR filter of the present invention is applicable to an adjustable mechanical member in a MEMS device which can be modeled as single mode second order system characterized by a resonance frequency xcfx890 and damping constant xcex6 less than  less than 1, i.e., a highly underdamped, single mode, second order system.
In embodiments of the invention, the MEMS device may be an optical micro-electromechanical switch. In some embodiments, this may be a tunable laser, such as an edge emitting tunable laser, or a vertical cavity surface emitting tunable laser, or VCSEL. In embodiments of the invention, the adjustable mechanical member in the MEMS device may be a cantilever arm, used to adjust a length of a Fabry-Perot microcavity in the tunable laser. In other embodiments, the adjustable mechanical member may comprise a mirror.
The invention includes a method of suppressing ringing in the mechanical component of an optical micro electro-mechanical switch, wherein the mechanical component has a positive damping constant substantially less than unity. The method may comprise one or more of the following steps: applying a first part of an electrical signal to the mechanical component; after a delay of about one half of an oscillation period of the mechanical component, applying a second part of the electrical signal to the mechanical component to cancel the ringing in the mechanical component. In some embodiments, the oscillation period of the mechanical component is equal to a multiple of an inverse of a damped resonance frequency of the cantilever arm and a constant pi. In alternative embodiments, the second part of the electrical signal is applied after a delay of on or about eight microseconds. These and other embodiments shall be elaborated infra.